The invention discloses a wavelength-tunable photoelectric detector, which comprises a semiconductor substrate F-P (Fabry-Perot) cavity narrow-band filer and a p-i-n photoelectric detector bonded with the semiconductor substrate F-P cavity narrow-band filter. The invention also discloses an optical wavelength detection system based on the wavelength-tunable photoelectric detector. The system comprises an F-P smoothing cavity tuning control module, an optical wavelength regulating module, a photoelectric detector output current detection module and the wavelength-tunable photoelectric detector. The invention also discloses a method for detecting the optical wavelength by the system. According to the invention, the optical wavelength detection system and the method thereof with the advantages of low cost, high integration, small size and portability are realized.